Project Summary End stage renal disease (ESRD) is among the ten leading causes of death for Americans, and its incidence and prevalence are rising, especially among non-White groups. Kidney transplantation is the most effective treatment option for many Americans, but the number of Americans needing kidneys is currently much larger and rising much faster than current transplant levels. Patients who seek transplants have one of two options: wait for a kidney from a deceased donor to become available, or obtain a transplant from a living kidney donor. Deceased donor kidney transplant levels are projected to grow little over time, constrained by population aging and mortality patterns, but living donation donor kidney transplantation (LDD KT) holds the prospect of substantial growth if healthy population members are willing and able to donate. Unfortunately, there are large and persistent racial and ethnic disparities in LDD KT rates that compound disparities in rates of ESRD. Prior research hypothesizes that differential access to healthy, compatible donors in candidates' social networks may explain racial disparities in usage of LDD KT. However, a limitation of this work is that it focuses on those who are evaluated for donation, not the many members of transplant candidates' social networks who could be evaluated for donation, but are not. We propose a multi-center study to collect novel data on transplant candidates' social networks and to test promising social interventions that could reduce barriers to LDD KT. Based on qualitative interviews and a pilot survey of 72 transplant candidates we previously collected in a large transplant center, we suspect that the differential access hypothesis does not hold, and that there are promising points of social intervention for researchers to reduce racial disparities in LDD KT. These pilot data show large LDD KT underutilization for all candidates, and that Black candidates have access to promising living donors at higher rates than White candidates. Based on these findings, we hypothesize that the primary barrier to eliminating disparities in LDD KT and promoting greater utilization of LDD KT for all groups is social, not biomedical, in origin. In this proposal, we will extend our prior work to develop and test evidence based, randomized social network interventions that will target social barriers to LDD KT and follow up with candidate medical records to evaluate the efficacy of these interventions. Specifically, we will compare a control group of candidates to those assigned to two treatments that we will pilot and test: a) a search intervention where a subset of candidates is coached to approach promising family members that seem to be underutilized based on our pilot data, and b) a rhetorical intervention where we encourage a subset of candidates to use scripts for discussing transplantation with family members that we find to be effective in survey vignette experiments and focus groups. With eighteen month medical records follow up of all candidates and the large amount of data we will obtain on their social networks, we will assess the social barriers that lead to underutilization of LDD KT, how those factors vary by race, and how they can be reduced through promising social network interventions. LDD KT has substantial potential to solve public health challenges around the growing prevalence of ESRD, and the basic and applied knowledge that we will develop as part of this proposal will help to unlock this potential.